This invention relates to blood pressure measurement devices, and particularly to blood pressure measurement devices that function automatically.
As is well known, the blood pressure of an individual varies during each ventricular heart beat from a high or systolic pressure to a rest or diastolic pressure. Such pressures are typically 120 millimeters of mercury (mm Hg) and 80 mm Hg for a healthy adult.
In the past, blood pressure measuring devices or sphygmomanometers were almost exclusively used by doctors and medical technicians (collectively called testing persons in this document) because of the difficulty in ascertaining accurate blood pressures of a patient. Such a standard sphygmomanometer consists of a pressurizing cuff which is placed over the patent's upper arm in juxtaposition to the patent's brachial artery. The cuff is then inflated by use of an air bulb while an analog dial gauge display, or a column of mercury, shows the pressure of the cuff. The cuff is inflated to completely occlude the flow of blood in the artery and the testing person listens with a stethoscope to ascertain this fact. By gradually lowering the pressure in the cuff, the testing person listens for the first sounds associated with arterial blood flow, known as the Korotkoff sounds. The cuff pressure at this point corresponds to the patient's systolic blood pressure.
By further reducing the cuff pressure, the testing person continues to hear surges of blood flowing through the artery during times when the blood pressure is greater than the cuff pressure, with occlusion of the arterial blood during the period of time that the blood pressure is lower than the cuff pressure. When the cuff pressure is reduced to a point where the surges are no longer heard (i.e., no arterial occlusion), the diastolic blood pressure reading is taken. Thereafter, the cuff is completely deflated, concluding the blood pressure measurement. In order to guarantee accurate results, the testing person must be well trained and familiar with the nature of the Korotkoff and other sounds typically heard through the stethoscope.
The last few years have seen a great increase in the public's awareness to the importance of careful monitoring of blood pressure in the avoidance of heart attacks and strokes. A great number of people have purchased sphygmomanometers for personal use without the requisite training and experience necessary to achieve accurate results. The present invention provides a compact, easily operated blood pressure measuring device which requires little skill or experience to operate and provides highly accurate results.
Although a number of prior art references disclose blood pressure monitoring devices which automatically determine systolic and diastolic pressures, none disclose or suggest the particular techniques utilized in the present invention including the use of a pressure transducer coupled to an analog amplifier which in turn is regulated by a sample and hold and logarithmic (log) converter for producing an output signal to accurately determine the occurrence of systolic and diastolic blood pressures. In particular, the present invention can be used with various individuals having much different blood pressure characteristics as well as body sizes while still providing accurate readings.
The present invention further provides control logic circuitry which automatically controls the sampling and holding of the received analog signal as well as controlling the operation of both a systolic and diastolic display. The present invention further uses the pulsating portion of the transducer blood pressure signal for determining which readings correspond to the systolic and diastolic pressures.
Although U.S. Pat. No. 4,078,551, Wohltjen et al discloses a sphygmomanometer having a pulse detector coupled to a pressure transducer to detect the superimposed electrical pulses for determining systolic and diastolic pressure measurements, it does not disclose or suggest the use of a sample and hold circuit in combination with a log compensation circuit under the control of control circuitry for providing a feedback control signal to the received pressure signal so as to be usable with various patients. Furthermore, Wohltjen et al does not disclose or suggest use of a dual display in which one of the dual displays constantly monitors the pressure within the pressurizing cuff used to make the physical measurements of the blood pressure.
Other prior art references such as U.S. Pat. No. 3,978,848, Yen et al, discloses a blood pressure measuring apparatus which utilizes two transducers, namely a blood transducer and a sound transducer, wherein the latter transducer is used to electrically "hear" the Korotkoff sound of inrushing blood at the time that full occlusion of an artery is first withdrawn, thus representing systolic pressure. This technique is of course different than that utilized in the present invention. This reference also neither discloses nor suggests the sample and hold and logarithmic feedback control system used in the measuring process of the present invention.
Another prior art reference; namely, an article in Medical Electronics by Looney, J. entitled "Blood Pressure By Oscillometry" (April, 1978, pp. 57-63), utilizes the pulsating or oscillometric pressure associated with a person's heartbeat to determine a maximum amplitude associated with minimum cuff baseline pressure so as to determine the mean arterial pressure. The oscillometric signal is not used to directly determine the time of the occurrence of systolic and diastolic pressures but is used to determine its maximum amplitude corresponding to mean arterial pressure and then extrapolating therefrom to calculate the systolic and diastolic pressures. The present invention clearly presents a determination of a systolic pressure occurrence when the fluctuating pulse pressure output exceeds the threshold detector so as to allow the analog to digital converter to measure a systolic pressure at the first occurrence of this output. The diastolic pressure occurs at the time that the threshold value is no longer maintained. It thus represents a departure from the disclosure in the Looney article.
U.S. Pat. No. 4,154,238, Link, discloses an apparatus and process which uses the second time derivative of the oscillometric waveform for determining the occurrences of systolic and diastolic pressures. According to the reference at column 2, lines 31-44, when the applied cuff pressure is approximately between the diastolic and systolic pressures of the blood vessel, there exists a negative spike in the second derivative. This negative spike essentially disappears when the applied cuff pressures correspond to diastolic and systolic pressures. Such time derivatives of the pulsatable effects generated by the blood vessels to determine the occurrence of systolic and diastolic pressure are not utilized in the present invention. This reference also neither discloses nor suggests the sample and hold and logarithmic compensating circuitry of the present invention.
Other references which were cited during the preparation and prosecution of the parent application are believed to be of lesser relevance, including U.S. Pat. Nos. 3,937,004, Natori et al; 4,063,551, Sweeney; and 3,391,691, Young.
In addition to the prior art cited, a commercial blood pressure measuring apparatus comprises a large bulky unit incorporating a chair, an automatic pressurizing cuff, and a large digital display screen. The drug store blood pressure measuring apparatus operates similar to the method traditionally used by doctors using ordinary sphygmomanometers and stethoscopes. A microphone is positioned in the pressurizing cuff and differences in sound output corresponding to total artery occlusion, partial occlusion and free blood movement is sensed by circuitry in the device to determine the systolic and diastolic pressure points. Additional components are necessary to determine the pressure of the cuff at these points so the microphone is used as a sensing device rather than as a measurement device.
This device is often located in well traveled areas of stores in order to attract prospective users. This can result in inaccurate blood pressure readings, as an individual is often excited and nervous about the presence of many other people around him or her. The present invention besides being easily carried by a person at all times, operates in a manner much different from these machines. The present invention directly utilizes the electrical output from the pressure transducer to determine the systolic and diastolic pressure.